Scientists have decoded the world’s oldest human DNA sequence, beating the previous record by almost 300,000 years, and at the same time confusing what we know of our early relatives.

Published in Nature on Wednesday, the study found that bone fragments from the Spanish cave Sima de los Huesos had less genetic similarity with European Neanderthals than with Denisovans, a human species believed to have resided exclusively in Siberia, reports National Geographic.

“The fact that they show a mitochondrial genome sequence similar to that of Denisovans is irritating,” says the lead author of the study, Matthias Meyer of Max Planck Institute. “Our results suggest that the evolutionary history of Neanderthals and Denisovans may be very complicated and possibly involved mixing between different archaic human groups.”

Meyer added that the DNA was preserved thanks to the cave’s stable temperatures, and that new advances in gene-sequencing technology played a great part in making the discovery possible.